1. Field of the Invention
This invention relates to a process for producing hyaluronic acid by using microorganisms.
Hyaluronic acid, one of such expensive glycosaminoglycans as chondroitin sulfate and heparin, is widely distributed in connective tissues of mammalians in only small quantities and is also known to present in microorganisms.
Highly pure hyaluronic acid preparations extracted from the aforementioned sources are highly viscous, effectively retain the moisture and have wound healing properties, so that they have been extensively in use as cosmetic constituents, supportive media in ophthalmic surgery and remedies for joint inflammation.
2. Description of the Prior Art
Conventionally, hyaluronic acid has been obtained industrially by extraction from rooster combs, bovine joints or whale cartilages. In addition, a process of obtaining hyaluronic acid from microorganisms has been disclosed in the Japanese Patent Laid-Open No. 58-56692 in which bacteria capable of producing hyaluronic acid are cultured and hyaluronic acid is purified from the culture.
However, the above-mentioned method of extracting hyaluronic acid from the animal tissues has various disadvantages and it is difficult to obtain hyaluronic acid effectively and in abundance by using this method.
For example, hyaluronic acid is present in the tissues in only tiniest traces and furthermore, it forms a complex with proteins or other mucopolysaccharides, therefore, complicated and delicate purification processes including procedures for removing proteins and for isolating other mucopolysaccharides are indispensable to obtain pure hyaluronic acid. In addition, hyaluronidase is often found in the extracting process of this method, which results in degradation of hyaluronic acid during the extracting process to give hyaluronic acid having a low molecular weight which brings disadvantageous properties such as poor moisture retaining capacity and low viscosity.
On the other hand, the method of purifying hyaluronic acid from the culture of bacteria capable of producing hyaluronic acid has an advantage that the purification process tends to be simple as compared to the aforementioned method for extraction from the animal tissues, since a protein-free medium is used for culturing bacteria capable of producing hyaluronic acid in the culture method to obtain hyaluronic acid.
However, even this method has a disadvantage that only low molecular weight hyaluronic acid can be obtained and the amount of hyaluronic acid produced per culture volume is low, since hyaluronidase is excreted by bacteria capable of producing hyaluronic acid during the culture.